1. Field of the Invention
The present invention relates to a method of forming a row of piles to form a wall, such as a retaining wall, for underground excavation by applying continuous packed-in-place mortar to form the pile, and by employing an earth auger device for use in the method.
2. Description of the Prior Art
In the prior art, to form piles, pile holes are excavated by an earth auger, and mortar is poured into the pile holes from the lower tip of the auger while it is being pulled out of the hole. This process is referred to as forming packed-in-place piles. This operation is repeatedly carried out to form a row of piles to form a wall and is extensively employed because of minimal noises and vibrations at the time of execution and because of its workability and economy.
The above-mentioned row of individual piles, in which a number of piles are joined with one another to form a retaining wall, poses a problem with respect to providing a watertight arrangement. To overcome this, attempts have been made to provide a watertight connection between the piles. The process considered most effective includes forming an intermediate pile between two previously-formed and spaced-apart outer piles, then injecting mortar from inside of the intermediate pile towards the outer piles, and then the earth between the outer piles and the intermediate pile is removed to form a hollow channel into which pile-forming mortar flows to form wing-shaped extensions to connect all the piles.
With respect to this process, several modifications have been proposed in the prior art. However, these processes have certain disadvantages, including difficulty in forming good watertight wings. For example, in Japanese Patent Publication No. 16,534/1973, an intermediate hole is excavated between previously-installed and spaced-apart concrete foundation piles driven into the ground, with the center of the intermediate hole being displaced outwardly from a line joining the centers of the previously-installed foundation piles. Then, a water-injecting excavation device is inserted into the intermediate hole to inject muddy water through a water-injection nozzle thereof towards the foundation piles to remove earth and sand between the intermediate hole and the foundation piles so that a communication channel is formed. Thereafter, the foundation piles are washed, and mortar is poured into the intermediate hole and the communication channel to form a sheathing body which is watertight and connects the foundation piles with each other. In this process, the excavation of the center hole and the pouring of mortar requires two separate steps. In addition, since bentonite muddy water is used to excavate the intermediate hole and to remove earth and sand, it is necessary to wash the foundation piles in order to provide a watertight connection between the foundation piles and the sheathing. However, because of the presence of water, the quality of the pile-forming mortar is decreased. In addition, a large quantity of water and work is required because the washing step must be carefully accomplished not to cause damage to the holes before the pouring step.
In addition, in Japanese Patent Laid-open No. 28,118/1975, which is an application by the same assignee as the present invention, an advance over the above-mentioned prior art is provided, in that washing of the foundation piles after excavation of an intermediate hole is not required. However, mortar is poured through an auger tip into a hole excavated between foundation piles, and thereafter, with a separate system of injection, cement paste is jetted from inside of the pile-forming mortar towards the preceding piles to cut away and remove earth between the intermediate hole and the foundation piles, and the thus-removed earth is replaced by a cement composition. The removal of earth by the injection of cement paste and the replacement thereof with the cement composition must be completed while the mortar poured into the intermediate hole is green enough to allow it to flow towards preceding piles, and consequently, a time constraint is imposed on this two-step operation. However, in this method, complete replacement of the earth and sand with the cement composition is difficult, and there is no assurance that a complete watertight connection has been provided.
In another prior art arrangement disclosed in Japanese Patent Publication No. 7526/1978, there is provided an arrangement wherein an earth auger or the like is used to drill, and a jet nozzle at the lower tip thereof injects grouting chemicals into neighbouring earth and/or preceding piles while rotating the auger and upwardly pulling out the earth auger. The chemicals penetrate and solidify the portions of surrounding earth around the intermediate pile in a radial formation, thereby forming a grouted soil sheathing body between the piles. In this arrangement, the auger has a jet nozzle extended from the shaft between flights of screws, and hence, the jet nozzle tends to become clogged with the excavated earth, and in some cases, stones or the like hit the nozzle to damage it during the excavation. Accordingly, this arrangement is rather impractical.